The purpose of this study is to define the role of biomarkers in photodynamic therapy of Barrett's esophagus. Barrett's esophagus is felt to be the predisposing condition for the most rapidly increasing cancer in Caucasian males. This is a randomized prospective trial to determine the effect of photodynamic therapy on biomarkers in Barrett's esophagus and to determine the role of biomarkers in predicting response to therapy. Preliminary studies have indicated that photodynamic therapy appears to be more effective in patients who do not have specific biomarkers. In addition, it appears that patients who undergo photodynamic therapy may have improvement in histology without improvement in biomarkers. Photodynamic therapy may induce mutations in certain genes even in normal appearing tissue. It is the goal of this protocol to determine the effect of photodynamic therapy on biomarkers that have been established to be predictors of progression to neoplasia in Barrett's esophagus. These biomarkers will include assessment of cell proliferation, ploidy, p53 expression, p53 mutations, P16 promoter hypermethylation, P16 loss, and P53 loss. Methods of assessment will include denaturing high pressure liquid chromatography, image cytometry, fluorescent in situ hybridization, and immunohistochemistry. Patients with and without biomarkers will be randomized to receive photodynamic therapy and a proton pump inhibitor or a proton pump inhibitor alone. Patients treated with photodynamic therapy will receive standard dosages of sodium porfimer (2 mg/kg) and photoradiation (130 J/cm fiber) using a balloon light delivery system. Patients will have their biomarkers assessed at six month intervals. Biological sampling will be done by biopsy and cytology to enhance sampling of the mucosal surface. In addition, primary cultures of Barrett's esophagus and squamous epithelium will be assessed for mutagenesis after photodynamic therapy in vitro to determine the rate of mutagenesis of p53. It is hoped that this study will help to define the role of photodynamic therapy in mucosal ablation of Barrett's esophagus in terms of patient selection and biomarkers that may predict response to therapy. These observations can be extended to other forms of ablative therapy in future studies.